Balanced signals are usually utilized in telephony technology, these signals being distinguished by the voltages in both conductors in a conductor pair being equally as great but of opposing polarity. In analogue-digital conversion of a balanced signal it is known first to convert it to an unbalanced signal and thereafter to convert the unbalanced signal to a digital signal. In the balance-unbalance conversion, half the dynamic range is lost however, since the signal voltage is limited by the feed voltage. The useful signals will also be distorted during the conversion, due to lack of linearity in the balance-unbalance converter.
It is therefore desirable to enable the analogue-digital-conversion of a balanced signal without first converting it to an unbalanced signal. One method for this is to utilize a separate A/D converter for each of the signal conductors of the balanced signal, and to connect the A/D converter outputs to a digital difference former. An apparatus for carrying out this method will be relatively voluminous and expensive, however.